I am looking to build an inflatable bladder with welded polyéthylène bag.I did many trials and had difficulties to get the bladder sealed perfectly, at some points of the welding line.
Basically I tried to duplicate this technique
https://www.youtube.com/watch?v=STj0eqDpafoHaving build a split mold, I was wondering if I could build a core with expandable PU foam on both side of the mold, then glue the two foams together to get a core that has the perfect inner shape of my mold.
I think some bike makers use this kind of core but in PS to build bike frame.